Return a rank-2 array of spline function values (or spline derivative
values) at points given by the cross-product of the rank-1 arrays x and
y. In special cases, return an array or just a float if either x or
y or both are floats. Based on BISPEV from FITPACK.

Parameters:

x, y : ndarray

Rank-1 arrays specifying the domain over which to evaluate the
spline or its derivative.

tck : tuple

A sequence of length 5 returned by bisplrep containing the knot
locations, the coefficients, and the degree of the spline:
[tx, ty, c, kx, ky].

dx, dy : int, optional

The orders of the partial derivatives in x and y respectively.

Returns:

vals : ndarray

The B-spline or its derivative evaluated over the set formed by
the cross-product of x and y.